In monitoring blood pressure, it is customary to insert one catheter to monitor arterial pressure and another catheter to monitor venous pressure. Each catheter is connected to a separate manually-operated rotary valve that can be positioned so as to couple the column of fluid in its catheter to a transducer or to means for withdrawing a sample of blood. Knowledge of the positions of the valves is necessary not only for the purpose of making a proper analysis of the varying blood pressures indicated by the transducer but also for the proper setting of low blood pressure alarms. For example, if the transducer is coupled to the venous catheter, the alarm should be set to sound at a much lower pressure than if the transducer is coupled to the arterial catheter. Neither alarm should sound if the valve is turned to shut off the blood pressure from the transducer so as to permit the withdrawal of a sample.
Whereas the positions of the valves can be determined by visual inspection, this can be confusing, especially if there is a change in operators. Furthermore, a manually operated system does not permit the use of monitoring instrumentation that is programmed to automatically set up alarm levels and to provide messages as to errors in valve settings when certain procedures are keyed into it.